That compiled the nvidia.ko module.
Next I copied the file
/var/tmp/portage/x11-drivers/nvidia-drivers-180.51/work/NVIDIA-Linux-x86_64-180.51-pkg2/usr/X11R6/lib/modules/drivers/nvidia_drv.so
to the directory
/usr/lib/xorg/modules/drivers/

Then insmod nvidia.ko
That allowed X to start at 2560x1600 resolution.

Then I did "rmmod nvidia" so that I could use the nv driver.

One problem remaining is that video looks blocky. Is that a problem with the nv driver or some problem with initializing the card?